1. Field of the Invention
The present invention relates to a driving apparatus and, more particularly, to a driving apparatus for switching energization of a coil in accordance with an output from a detection unit for detecting a magnetic pole of a rotor.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. H09-331666 (corresponding to U.S. Pat. No. 5,831,356) discloses such a technique that a sensor as a Hall device (hereinbelow, abbreviated to “sensor”) is provided for a stepper motor (hereinbelow, abbreviated to “motor”) to detect a rotational position of a rotor magnet.
According to such a technique, together with an ordinary step driving, a feed back driving for switching energization of a coil at proper timing according to a desired speed or load can be performed. Thus, the motor can be used in a wide speed region from a low speed region to a high speed region and, at the same time, a high output torque can be attained.
FIG. 9 is a diagram for describing an example of controlling an energization switching timing of each coil on the basis of sensor outputs in a motor having two sensors and coils for two phases. Such energization switching timing control can be achieved by, for example, a motor driving circuit (not shown). A description will be made hereinbelow on the assumption that the two sensors are an A sensor and a B sensor and the coils for two phases are an A-phase coil and a B-phase coil. When it is detected that an output of the A sensor has changed from a Low level (hereinbelow, abbreviated to “L”) to a High level (hereinbelow, abbreviated to “H”) at timing denoted by T1 in the diagram, the A-phase coil is subsequently energized in a + direction at timing denoted by T2 in the diagram, which is reached after the elapse of a preset time Ta1. After that, when it is detected that an output of the B sensor has changed from L to H at timing denoted by T3 in the diagram, the B-phase coil is subsequently energized in the + direction at timing denoted by T4 in the diagram which is reached after the elapse of a preset time Tb1. After that, such control that times (Ta2˜Ta4) and (Tb2˜Tb4) which are required until the energization switching of the coil is performed after an H/L inversion of the sensor happened are increased or decreased or are held to be constant is continuously made. According to this, it is possible to cause the motor to rotate acceleratedly, deacceleratedly, or at a constant speed against a rapid load change.